docs: def polyder(c, m=1, scl=1, axis=0):
      '''not quite a copy of numpy's version because this was faster to implement.
      '''
      c = list(c)
      cnt = int(m)
  
      if cnt == 0:
          return c
  
      n = len(c)
      if cnt >= n:
          c = c[:1]*0
      else:
          for i in range(cnt):
              n = n - 1
              c *= scl
              der = [0.0 for _ in range(n)]
              for j in range(n, 0, -1):
                  der[j - 1] = j*c[j]
              c = der
      return c